Problem: William eats at a cafe and the cost of his meal is $\$25.00$. He would like to leave a $20\%$ tip. What is his total bill including tip?
The tip amount is equal to $20\% \times \$25.00$ We can find the tip by first calculating a $10\%$ tip and then multiplying that number by two. To calculate a $10\%$ tip, move the decimal point in $\$25.00$ one place to the left. $10\%$ $\times \$25.00$ $\$2.50$ To calculate a $20\%$ tip, multiply the $10\%$ tip amount by two. $20\%$ $\times \$25.00$ $\$2.50$ $ \times 2 = $ $\$5.00$ The cost of the meal plus the amount of the tip will equal the total bill amount. $\$25.00 + \$5.00 = $ $\$30.00$ The total cost of the bill is $\$30.00$.